Laptop interfering with network

In my house I have 2 routers, a Netgear DG834GT connected to the phone line and a 4th gen Airport Extreme.

Netgear is 2.4ghz G and on Auto channel selection and used mainly for connecting the AE to the internet and servicing anyone who comes around needing a connection.

The AE is on 5ghz N and split between my devices but also setup for a separate network thats filtered for the kids to use when they come around.

Problem is that my youngest has brought his laptop around (some sort of Sony Vio) running W7 Home premium but it won't connect to the kids network even though it sees it, I've been through and done a new connection on the laptop and that didn't work so had to connect him on the Netgear. Now the other problem is in that doing that all the other devices (MBP, MM & WDTV) lose their internet connection when he's using his laptop, all my devices show their connected but every 30 seconds or so I can see the connection drop, then searching, connecting again then dropping.

Anyone got any ideas for me to try next time he come around with his laptop.

Thanks and hope it makes sense.

You're using Auto-channel select and auto-mode select on the router?

I've had issues with those in the past going bannana's, fix the mode and the channel and see what happens.

cheers, will do that now and see when they come again.